Axial piston pump with balanced drive plate



Sept. 11-9 1962 R. P. LAMBECK 3,053,197

AXIAL PISTON PUMP WITH BALANCED DRIVE PLATE Filed Deo. 24. 1959 2 Sheets-Sheet 1 F/GJ A TTOPNEV Sept 11, 1962 R. P. LAMBECK 3,053,197

AXIAL PISTON PUMP WITH BALANCED DRIVE PLATE Filed Deo. 24. 1959 2 Sheets-Sheet 2 LMd /NVENTOR RAYMOND l? LAMBEQK United States Patent O 3,953,197 AXIAL PISTON PUMP WiTH BALANCED DRIVE PLATE Raymond P. Lambeck, Birmingham, Mich., assigner to United Aircraft Corporation, East Hartford, Conn., a

corporation of Delaware Filed Dec. 24, 1959, Ser. No. 861,832 6 Claims. (Ci. 10S-162) This invention relates to piston pumps and more part-icularly to fluid pumps having a rotor carrying the pistons and in which the pistons reciprocate.

It is a feature of this invention to provide a pressurebalancing arrangement whereby fluid under pressure is directed from a high-pressure source through a fixed laminar restriction and to the antipurnping end of the piston where it is conducted to a reaction surface such as a bearing so that bearing forces are reduced.

It is another feature of this invention to provide the above pressure balancing in an axial piston pump having a fixed reaction bearing surface.

It is another feature of this invention to provide a predetermined spacing between the piston and piston walls to form a fixed restriction which connects in turn to an annulus around the piston for subsequent communication with passages in the piston rod which lead to the reaction surface.

It is still a further feature of this invention to provide means for maintaining a fluid film between the fixed reaction bearing surface and unitary drive plate surface so that the high friction normally associated with bearing surfaces is reduced to a minimum during starting regimes of the pump.

It is another feature of this invention to provide a unitary drive plate that has axial motion relative to the fixed thrust bearing so that relative distance therebetween forms a variable fluid escape path.

It is another feature of this invention to provide an axial piston pump having a thrust member which operatively receives the antipumping ends of the piston rods and includes a surface comprising a plurality of pressure wells receiving the metered fluid under pressure for pressure balancing the pump, these wells forming pressure chambers in relation to the adjacent flat bearing or reaction surface.

[It is a further feature of this invention to provide pressure wells which are so located with respect to their respective piston rods such that the resultant center of pressure is coincident with or radially spaced outwardly with respect to the location of the major force resisting this pressure load.

It is a further feature of this invention to provide a plain axial bearing and a plain radial bearing with the radial bearing being particularly aligned to avoid eccentric loading.

These and other features of this invention will become readily apparent from the following detailed description of the drawings in which:

FIG. l is a detailed crosssectional illustration of the pump assembly embodying the features of this invention;

FIG. 2 is an enlarged detailed cross-sectional showingV ice FIG. 3 is an enlarged detailed showing of the bottom of the unitary thrust plate; and

FIG. 4 is a partial showing of a side view of FIG. 3 schematically illustrating the tilt-balancing forces.

Referring to FIG. l, the pump is shown as having an upper casing 1t) and a lower base casing 12 from which protrudes at the left side a toothed member 14 for driving the pump. The member 14 includes a shaft 16 having splines 18 for driving the unitary thrust or drive plate 20. The unitary thrust plate 20 includes a number of peripherally spaced ball-receiving sockets 22 which receive the balls 24 at the antipumping end of each piston rod 26. The unitary drive plate adjacent its left end includes an elongated spline Sli which also through the spline 32 drives a coupling 34 carrying a beveled gear 36. The beveled gear 36 engages a cooperating gear 38 for driving the shaft extension 40 which via the splines 42 drives barrel-like rotor 44. The axis of the rotor 44 is at an angle with respect to the drive plate 20 and its adjacent bearing 120 such that as the barrel rotates the piston rods 26 are reciprocated thereby inducing a pumping motion to the pistons 50. A valve plate 60 is suitably held into engagement with the top pumping end of the rotor 44 and is held against continued rotation by means of a spline connection 62 leading to a control shaft 64. The control sha-ft 64 is mounted on suitable bearings 66 and 68 and carries a pinion 70'which is engaged by one or more racks 72 which can in turn be actuated by a suitable servo unit. The servo unit is intended to rotate the valve plate 60 so as to interconnect one or more pistons either to the inlet or the outlet 82 or to connect certain pistons to each other. A control mechanism of this type is more clearly illustrated and described in copending patent application Serial No. 821,180, filed June 1S, 1959, byv Richard N. Sullivan.

With high pumping loads, normally, the antipurnping end of the piston, piston-rod assembly would have to be engaged and supported by thrust bearings of substantial Weight and size. However, provision is made for pressure balancing the assembly so that a lightweight plain bearing can be utilized in placev of the -rnuch heavier antifrictiontype ball bearingsl or the like. To thisV end, each piston 50 (see also FIG. 2) has a land portion 90 which is meticulously .machined and lapped With respect to its adjacent cylinder wall so as to for-m a first fixed orifice 92, better seen in FIG. 2. The fixed orifice 92 thus formed is continuously wiped during the piston reciprocation which tends to make it a self-cleaningV capillary' restriction. The restriction is of a predetermined size and length so that under maximum pressure operation of the pump' a predetermined pressure drop will occur thereacross. During operation', high-pressure fluid from the pumping Chamber 94 flows through the fixed restriction 90V andV thence to an annulus 96 leading to a transversey passage 98 in the piston. This passage in turnl connects with a passage 100 drilled centrally of the piston rod 26. The ballV joint 24 at the antipumping end of the piston rod 26 includes a flat portion 104 so that continuous communica'- tion is provided with the drilled passage 106 in the socket 22, regardless ofthe rotary or tilted position of the pistonY rod in the pumping cycle.

rThe bottom or reaction `face (FIG. 2) 110 of the unitary drive plate 20 contains a plurality of circular wells or recesses 112 which, as seen valso in iFIG. 3, may have their centers eccentrically located or spaced in an 3 outward direction with respect Ato the axis ofthe bleed passage 106. The wells or recesses 112 form pressurebalancing areas which .form a liquid-type bearing surface to reduce the friction loading on the -adjacent cooperating plain bearing 120.

The construction of the pump is such that there is permitted a limited relative axial movement of the thrust drive 20 with respect to the plain bearing 120 so that there is provided therebetween a variable orice depending upon the pressure and the loading of the pump parts.

The pressure wells 112 and the remaining radial areas of -the juxtaposed surface 11() and Ithe bearing 12.0 form the total balancing force depending upon the pressure across this region. Thus, the maximum balancing pressure will occur in the wells 112 but there is a drop across the cooperating surfaces as the leakage flow passes outwardly to the substantially low casing pressure. The total force is an integration of the particular pressures over their respective areas which, at the balanced position of the parts, are equal to the total |force acting on the piston lheads. Thus, the variable orilice formed by the space in between the reaction surface 110 of the drive plate 20 and the bearings 120 determines the outflow of the bleed iiuid and hence the pressure level necessary to achieve equilibrium and balancing.

For example, if the combined iluid pressure in the well and between the cooperating surfaces is at a level whereby the force acting on the thrust bearing is less than the force generated by the piston, the unitary drive plate will be urged toward the thrust bearing and effectively reduce the area of the Variable orifice which effects a reduction in -uid flow and hence builds up the pressure in the well and the cooperating surfaces until the forces created by this newly increased pressure will substantially equal and cancel out the forces generated by the piston. And conversely should the combined uid pressure in the well and between the cooperating surfaces generate a 'force which is greater than the force generated by the pistons, the unitary drive plate will be urged away from the thrust bearing, effecting an increase in effective area of the variable orifice so as to increase V.the ow therethrough and hence reduce the pressure in the well 4and cooperating surfaces. In this manner the movement of the unitary drive plate with respect to the thrust bearing will automatically adjust itself to maintain a iluid pressure level in the well and between the cooperating surfaces so that the forces generated thereby will substantially match or equal the forces generated by the piston.

It is thus apparent that during starting, the unitary drive plate will be moved away from bearing 120 so as to form a lubricant film immediately to avoid starting friction.

The bleed liiuid from the radial variable orifice can iiow through a chamber 130 leading to the casingl Another passage 132 is provided for receiving leakage fluid from the annular chamber 134 leading from. the inside or axial end of the variable orifice.

Returning to FIG. 1, the radial pump forces are absorbed through an annular plain bearing 150 which engages an outer peripheral surface 152 on the drive plate Z0. The size of the bearing 150 is materially reduced by locating its supporting pedestal l:154 in a plane containing lthe centers of pivotation of each of the balls 24 at the antipumping end of the piston rods 26. In this way, the radial loads are symmetrical, thu-s avoiding any cooking tendency which would require larger and higher strength bearings and supports. With this particular bearing arrangement and the pressure balancing, the size and weight of the pump of this invention are materially reduced.

Another advantage of the radial bearing described is 'that the rotor of the pump does not have to absorbY these radial loads. Instead the side loads are taken at the antipurnping end of the connecting rods so thatpistonV wear is avoided since they are not subject to eccentric loading.

In order to further reduce the weight requirements of the pump assembly, reference is made to FIGS. 3 and 4. As previously stated, the pressure wells 112 which are disposed about the center of the unitary drive plate 20 have their cen-ters radially spaced from the centers of the bleed passages 106 leading thereto. This moves the total center of pressure radially outwardly so that on the pumping side of the thrust plate, the resisting force will be located inwardly thereof as seen in FIG. 4. This resisting force and the center of pressure produce a force couple which can be balanced readily by a relatively small balancing force, as indicated in FIG. 4, because of its relatively lange moment arm. It should be noted, however, that the center of pressure will travel radially as the valve pla-te 60 is adjusted since only certain pistons -will be contributing to the iinal pumping output. In any ca-se, the center of pressure should be coincident with or outboard of the major resistance vector.

A-s a result of this invention, it will be apparent that an extremely lightweight pump has been provided which can be made relatively small in size. This compactness makes it readily adaptable for aircraft and missiles where weight saving is of the essence. Thus, the bearings are reduced materially in size and weight permitting the entire structure to be manufactured at low cost.

Although one embodiment of -this invention has been illustrated and described herein, it will be apparent that various changes may be made -in the construction and arrangement of the various parts without departing from the scope of lthe novel concept.

I claim:

l. In a multiple piston pump having a rotatably mounted rotor, a plurality of cylinders formed in said rotor, a corresponding number of pumping pistons mounted in lsaid cylinders, a plate member connected to the anti-pumping end of said piston, a bearing member having -a iirst bearing surface and a second bearing surface surrounding the first bearing surface, chamber means located between said bearing member and said plate means for receiving fluid from said cylinders so that said iluid acts on said lirst bearing surface, passage means extending through said piston including a fixed restriction connected `to said cylinders for communicating with'said chamber means, said plate member being movable rectilinearly with respect to said bearing member for defining a variable orifice, said varia-ble orifice serving to control the leakage of uid from said chamber means so thatvthe leakage lfluid acts on said second bearing surface, the combined rrst bearing surface and second bearing surface serving to counterbalance the thrust force created by said pumping piston, and means providing recesses in said plate member corresponding to said pistons respectively, for maintaining alignment of said plate member relative to said bearing member, said recesses being disposed eccentrically outwardly relative to the resultant axial forces of their respective pistons.

2. In a multiple piston pump according to claim l, wherein said fixed restriction is defined by each piston having a portion of its length of reduced diameter smaller than that of its cylinder communicating with said passage means.

3. In a multiple piston pump according to claim l, wherein each piston has a rod connected thereto, each rod having an end remote from its piston connected to said plate member by a swivel joint.

4. In a multiple piston pump according to claim l, wherein each passage means includes a passage disposed transversely of said piston and a passage disposed axially of said piston.

5. In a multiple piston pump according to claim l, wherein each piston has a rod connected thereto, each rod having an end remote from its piston connected to said plate member by a swivel joint, and said passage means includes passages extending transversely of said piston, axially of said rod and through said swivel joint.

6. In a multiple piston pump according to claim 1 wherein each piston has `a rod connected thereto, each rod having an end remote vfrom its piston connected to said plate member by a movable joint, said passage means extending `through said piston, said rod `and said joint.

Doe May 13, 1941 Ruben Apr. 17, 1951 6 Dietiker Apr. 21, Klopp Feb. 7, Postel et al. May 13, Bauer Dec. 2, Henrichsen Sept. 1, Sherman Dec. 22, Lucien Dec. 22,

FOREIGN PATENTS Great Britain June 29, France Dec. 19, 

